Planar metamaterial sensor with graphene elliptical rings in transmission mode

A periodic planar metamaterial sensor in the terahertz band based on surface plasmon polariton resonances is proposed and studied. The unit cell includes four half-elliptical graphene rings located on a three-layer substrate including a SiO₂ layer, an air gap, and another SiO₂ layer. The embedded air gap between the two layers of SiO₂ improves the sensitivity of the sensor. Parametric study is performed, and the effects of the dimensions of the elliptical rings, the air gap thickness, and the Fermi energy of graphene on resonant frequency, sensitivity, and figure of merit (FoM) are investigated and graphically illustrated. The parameters of the sensor are optimized to provide a high sensitivity with a suitable FoM. By changing the refractive index of the sensing environment from 1.2 to 2, maximum sensitivity of 21.1 µm/RIU with FoM 5.14 is provided. The performance of the sensor is compared with previous works, and it is shown that a considerable improvement in sensitivity is achieved. The proposed sensor is suitable for biosensing applications.